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https://issues.apache.org/jira/browse/JAMES-2295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16547879#comment-16547879
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ASF GitHub Bot commented on JAMES-2295:
---------------------------------------
Github user mbaechler commented on a diff in the pull request:
https://github.com/apache/james-project/pull/127#discussion_r203391329
--- Diff:
server/queue/queue-jms/src/main/java/org/apache/james/queue/jms/ConsumerOptions.java
---
@@ -0,0 +1,42 @@
+/****************************************************************
+ * Licensed to the Apache Software Foundation (ASF) under one *
+ * or more contributor license agreements. See the NOTICE file *
+ * distributed with this work for additional information *
+ * regarding copyright ownership. The ASF licenses this file *
+ * to you under the Apache License, Version 2.0 (the *
+ * "License"); you may not use this file except in compliance *
+ * with the License. You may obtain a copy of the License at *
+ * *
+ * http://www.apache.org/licenses/LICENSE-2.0 *
+ * *
+ * Unless required by applicable law or agreed to in writing, *
+ * software distributed under the License is distributed on an *
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY *
+ * KIND, either express or implied. See the License for the *
+ * specific language governing permissions and limitations *
+ * under the License. *
+ ****************************************************************/
+
+package org.apache.james.queue.jms;
+
+import org.apache.james.queue.api.MailQueue;
+
+/**
+ * Provides additional options when creating consumers.
+ */
+public interface ConsumerOptions {
+ /**
+ * The empty consumer options.
+ */
+ static ConsumerOptions empty() {
--- End diff --
The rational is : it never changes so you can easily avoid useless object
creation.
The reason why Optional and Function uses methods for that is generic
handling.
see for example Optional :
```
public static<T> Optional<T> empty() {
@SuppressWarnings("unchecked")
Optional<T> t = (Optional<T>) EMPTY;
return t;
}
```
It allows to return the right Optional<T> type for the caller. They however
use a singleton anyway for the same reason I asked it.
In our case, the type is not generic so we don't need this extra complexity
but if you want to return a singleton with a method, I don't have anything
against it.
> JMS mailqueue deadlock when a single thread issue several consume
> -----------------------------------------------------------------
>
> Key: JAMES-2295
> URL: https://issues.apache.org/jira/browse/JAMES-2295
> Project: James Server
> Issue Type: Bug
> Components: Queue
> Affects Versions: 3.0.0, master, 3.0.1
> Reporter: Tellier Benoit
> Priority: Major
> Labels: bug
>
> This will lead to a dead lock:
> {code:java}
> MailQueue.MailQueueItem mailQueueItem1 = getMailQueue().deQueue();
> MailQueue.MailQueueItem mailQueueItem2 = getMailQueue().deQueue();
> mailQueueItem1.done(true);
> mailQueueItem2.done(true);
> {code}
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